1. Field of the Invention
The present invention is generally directed to a method and apparatus for inducing visual preception in persons suffering from blindness caused by retinal disease, pathology, or malfunction. Many causes of blindness, especially those involving occlusions or opacity in the optical pathway through the eye, have yielded to modern medical treatments, and vision can be restored to a great extent in a large number of cases. Indeed, the removal of cataract-occluded lenses is now a mere outpatient surgical procedure, and the substitution of plastic lens implants yields excellent results. Likewise, relief from secondary cataracts in the posterior capsule of the lens may be corrected using optical laser eye surgery in a noninvasive procedure requiring only minutes to complete.
Some diseases of the eye, however, cause blindness by attacking the light-sensing retina, causing blindness while the remainder of the optical pathway remains perfectly clear and functional. For example, the genetically transmitted disease retinitis pigmentosa gradually causes destruction of the rod and cone cells in the retina, resulting in eventual total blindness. It is interesting that this disease does not adversely affect the optic nerve, nor the neurons in the retina. It is known that other diseases affecting the retina likewise leave many viable neurons in the retina.
Recent research and development in the field of sensory deafness has shown that such deafness can be overcome, and intelligible hearing can be induced by direct electrical stimulation of the auditory nerve endings distributed along the basilar membrane in the cochlea of the inner ear. By properly filtering, processing and channeling spectral portions of the electrical audio signal analog of ambient sound to appropriate portions of the basilar membrane, significant word recognition can be achieved by individuals who were formerly completely deaf. These successful developments suggest that direct electrical stimulation of visual neurons should be able to provide at least some degree of visual cueing to persons suffering from sensory blindness.
2. Description of the Relevant Literature
Michelson, R. P., "Electrical Stimulation of the Cochlea," Gerald English's Otolaryngology, Harper and Row Publishers, Inc., 1980.
Potts, A. M., et al., "The Electrically Evoked Response of the Visual System," Invest. Ophy. (1968) 7:269-278.